The present invention relates to shredding-by-cutting of strips which have been cut of webs upon trimming the edges of such web.
Webs of interest are, for example, plastic webs, foils, vlieses, or the like, which are usually made as a continuous sheet having rather irregular edges. Therefore, it is customary to trim such web along the edges not only for the sake of appearance but also to establish a particular width. As a consequence, a continuous strip of more or less irregular width is being cut from each of the edges of such a flexible material. The transport speed of such a web, for example, through the trimming station is often rather high, and the cut-off edge strips, one from each side, have to be removed in some fashion, for example, for disposal as waste or for purposes of recycling. The particular edge strips are, in fact, as continuous as is the web from which they are cut, and it is cumbersome and impractical to store or dispose of these strips in that configuration. This is particularly true if recycling is required as further processing will require some form of dividing the strips into smaller portions. Even disposing of the strips as waste will require some form of fragmentation.
The removal of the strips from the trimming machine and the fragmentation of the strips appears on its face to be a fairly simple problem; surprisingly significant problems have arisen in practice, which not have been satisfactorily resolved.
Generally speaking, it has been attempted to run the strips in some fashion away from the trimming device and to cut the strips into small pieces, for example, by means of a device which basically includes an annular opening and a cutting device that moves across that opening. It was found, however, that these known devices do not properly cut very thin plastic foils or foils having embedded or consisting of woven textile cloth-like materials. Also, it was found that running the strips from the trimmer to a central cutting station over long distances and introducing the strips into the cutting device, frequently incurs interferences, is rather noisy and not very reliable as to consistency as far as the fragmentation desired is concerned. Amazingly enough, it has been observed that certain principles in the mode of operation of such devices pose the problem and are directly responsible for the unsatisfactory operation, which in cases, may result in a complete stoppage of the entire production line.
One of these detrimental principles of the known equipment and method is to be seen in that the strips are in some fashion moved by means of air flow, and are introduced in that manner into the cutting station. It was found that particularly very thin and very flexible strips have the tendency to vibrate to a considerable extents, so that individual strips may bunch and snarl. Particularly if the tubular guide for such a strip is curved and other irregularities in the cross-section of such a guiding tube produce considerable turbulence. Snarling and twisting is also the more pronounced the greater the number of strips which are being moved through the same conduit. As the strips emerge from the guiding tube, an air flow becomes inherently irregular producing local turbulence and, again, snarling and twisting may prevent smooth entry of the strips into the cutting station. This may lead to snarls, looping, coiling or sticking in some location ahead of the cutter proper and the cutting, in effect, is interrupted, while continuously additional strip material is fed into the snarl. For some reason, a snarled bunch may thereafter be pushed or moved for other reasons into the cutting station, and due to its size may, in fact, block the cutter which ultimately may result in a breakdown of that device. Also, even small snarls will be unevenly cut, and do, in fact, load the cutter irregularly so that it wears faster and the noise developed is necessarily larger.
The moving of thin flexible strips through a pipe by means of air currents is also disadvantaged because, on the basis of the flow dynamics and the physics underlying the phenomena, strips may stick to the walls of such a tube, so that they may not even emerge therefrom. Snarling, back up and bunching in the tube, finally blocking the tube completely may completely interrupt the operation. Snarling and other interferences may also lead to tearing of strips.
It was further observed that, for example, in the case of certain plastics, the air flow accompanying the passage of such plastic strips through the tube resulted in electrical charges which, in turn, enhence the tendency for the strips to stick to the tube wall.
It can, thus, be seen that there are basic, inherent problems in moving the strips to the cutting station through a confined space and by means of air flow.
Another principle of operation of the known methods and systems, which pose disadvantages, is to be seen in the cutting of these strips, particularly into short clippings or cuttings by means of a cutter drum, having an axis of rotation which extends transversely to the direction of movement of the strips and cooperating with counter blades oriented parallel to that axis of rotation. The cutter drum produces an air flow on account of its rotation which is directed against the direction of movement of the strips, so that the latter, in fact, are blown away from the opening into which the strips to be cut are to be introduced. Therefore, the strips must be forced into that opening by means of a counteracting, stronger air flow. This, in turn, means that the entrance to the cutter is subjected to two oppositely directed air streams, resulting inherently in considerable turbulence thereat, tending to snarl the strips.
It was further found that such cutter drums oriented transversely to the direction of movement of the strips to be cut, do not really cut the strips by the usual shearing action but, in fact, the strip is chopped. This is due to the fact, that the blades of the drum cutter and the counter knife are for all practical purposes, almost parallel oriented so that the piece to be cut is engaged almost over its entire width and in an almost uniform manner, so that the shearing operation is not a true cutting but, in fact, a chopping operation. Furthermore, it has to be considered that the cutter drum mounted in bearings inherently has position tolerances so that the several blades, i.e. the movable ones and the stationary ones, move past each other without engaging but with a minute gap between them. This means that thin foil or textile strips may be wedged into the gap without being cut, chopped, or otherwise separated. Furthermore, it was found that these drum cutters are rather noisy.
The German printed patent Application, No. 2,100,713, discloses a cutter of the type outlined above and having the stated disadvantages. The device serves particularly for chopping strips resulting from trimming the edges of metal strip. Air moves the cut strip into a channel to be engaged by a rotating toothed tool and placed under tension to tear off at the end of the channel. This particular arrangement is disadvantaged on account of the air flow feeding as outlined above. Moreover, thin foils may not necessarily tear and be cut at the channel ends. Moreover, there is a gap between the channel and the teeth on the tool, so that a flexible strip, if very thin, may enter the gap without being cut, torn, or otherwise severed. For this reason, this particular tool can simply not be used for cutting thin flexible foil strips or strips containing textile fibers. Clearly, this particular publication does not suggest any remedy for these deficiencies.
The same can be said with regard to other publications describing methods and devices for removing and cutting strips resulting from edge trimming. By way of example, the German printed patent application, No. 1,561,707, describes such a cutter but does not disclose any means by means of which the strips can be moved from the trimmer to the strip cutter over a fairly long distance.
The U.S. Pat. No. 3,397,377 describes edge strips resulting from trimming multi-layer paper sheets. Rotating cutters are disposed directly underneath the trim cutters, in the same plane, and have an axis of rotation extending transversely to the direction of movement of the cut-off and trimmed-off strip; the rotating cutters cut the particular strips into small pieces. This is a more or less integrated kind of device.
The U.S. Pat. No. 3,536,273, discloses the transport of cut-off edge strips resulting from trimming of the edges of a plastic foil and under utilization of tubes; any further cutting of the cut-off strips is not described in this particular patent. The same is true with regard to the German printed patent application, No. 2,212,279, which discloses, in addition, the suction of textile strips away from the trimming equipment.
The German printed patent application, No. 1,253,033, likewise discloses removal of a cut-off edge strip by means of air flow and through a corresponding duct, but nothing is disclosed in this particular patent concerning the cutting of strips into small pieces.
The German Pat. No. 1,125,259, suggests moving cut-off edge strips through a pipe by means of an air flow towards a chopper. This chopper has cutting blades, whose axis of rotation extends transversely to the direction of movement of the strips.